The invention concerns a machine, having a lateral channel and often termed air-ring blower, comprising an impeller provided with a central body to which peripheral blades are connected. The impeller is closed in a casing which defines a circumferential annular conduit, arranged on the external circumference of the casing, in which the impeller blades rotate. The annular conduit exhibits an intake mouth, through which a fluid is aspirated and enters the machine, and a delivery mouth through which the fluid is expelled from the machine itself. Both the impeller and the casing are normally made by moulding or pressing.
These machines can function either as vacuum pumps or as compressors. In the first case the induction mouth is connected to the environment where a depression is to be created and the delivery mouth is generally connected to the external atmosphere; while in the second case the induction mouth is generally connected to the external atmosphere and the delivery mouth is connected to the environment where an overpressure is to be created. In both cases the pressure at the induction mouth is lower than the pressure at the delivery mouth, so there exists a Δp between the zone where the induction mouth is and the zone where the delivery mouth is.
The annular conduit exhibits a first tract, which, following the advancement direction of the blades in the conduit, goes from the induction mouth to the delivery mouth, and a second tract, which goes from the delivery mouth to the induction mouth. The first tract has a transversal passage section having greater dimensions than that of the second tract. More precisely, each blade fits the second tract snugly, i.e. it passes at a very tiny distance from the internal walls of the second tract; preferably this distance is the tiniest possible, compatibly with friction problems, so as to prevent fluid passage between the two mouths through the second tract. Between the internal walls of the first tract and the blades a much larger free space is left, wherein turbulent fluid movement can take place.
During operation, the dynamic action of the blades generates a fluid current in the first tract of annular conduit from aspiration to delivery. The conformation of the annular conduit, and in particular the presence of the free space between the blades and the internal walls of the first tract of annular conduit is necessary in order for the motion of the blades to effectively give rise to a current of fluid from induction to expulsion.
The impeller is keyed on a shaft, which is usually set in rotation by an electric motor and rotates internally of the casing. At the lower part of the conduit the blades of the impeller rotate in, an annular slit is afforded which enable passage of the body of the impeller internally of the casing. Between the internal part of the annular slit and the body of the impeller as small a space as possible must be left, compatibly with the problem of friction, in order to prevent passage of fluid from the channel to the internal part of the casing where the impeller shaft is located.
The functioning of these machines, which is represented by the flow rate/head diagram, as well as by the angular velocity of the impeller, is strongly influenced by the size of the machine, and in particular the size of the lateral channel and the blades. The constructors therefore offer a wide range of machines, having different dimensions, each of which operates in a determined field of flow rate/head ratings demanded by the market.
For this reason a large number of moulds has to be made available, as well as a large number of components, for realising the parts of the various machines. This inevitably leads to a considerable increase in construction costs, warehousing for spare parts and machine maintenance.
The customer also has to face the need to change machines if, over time, his requirements change.
The main aim of the present invention is to solve the above-described problems, by providing a machine of the type described which can satisfy various operational needs, while keeping the base structure and thus considerably reducing construction costs and warehousing expenses for spare parts and maintenance.
A further aim of the present invention is to realise a machine in which performance can be optimised even in various operative conditions.
An advantage of the invention is that it attains the above-cited aims in a way which is constructionally simple and economical.
A further advantage is that the invention can be easily applied to known-type machines.
A further advantage is that the invention limits the danger of the impeller's seizing.
These aims and advantages and more besides are all attained by the machine of the invention, as it is characterised in the claims that follow.